If you are correct, the Python community would very much like to know under what circumstances you are correct, so that the problem can be mitigated or at least warned.

WHAT is a deceptively large range? It's possible that the built-in hashing functions are experiencing collisions for your data. A tuple of points: It hadn't occurred to me that with a such a small range an exhaustive test was load fille beninoise. Can you post us some sample code for the memoization function?